1. Field of the Invention
The present invention relates to an electrical connector device, and more particularly to an electrical connector device for an electrical system requiring electrical connection between rotatable members, such as an electrical system for an air bag system mounted in a steering wheel of a vehicle.
2. Description of the Prior Art
There have been known air bag systems which include an air bag normally collapsed to be housed in a steering wheel or another vehicular member and inflatable to provide cushioning against damaging impacts which passengers would otherwise be subjected to in automobile accident. Such air bag systems include a collision sensor which is attached to a vehicle frame and, upon detection of a vehicle collision requiring air bag inflation, delivers a signal to an actuator for detonating an explosive in order to release or produce a pressurized gas which, together with air, is introduced into the air bag to inflate the latter.
The air bag is normally housed centrally in the steering wheel with the actuator and gas generator disposed adjacent to the air bag, and the collision sensor is located remotely from the air bag. Because the steering wheel and steering shaft are rotatable with respect to the vehicle frame, the collision sensor and the actuator are required to be electrically connected to each other by a suitable electrical connector means which provides electrical connection between mutually rotatable members.
One such known connector means comprises a slip ring mechanism including a slip ring and a brush which are movable relative to each other and held in sliding contact with each other. While the slip ring mechanism allows the slip ring and brush to move angularly through a relatively large angle, contacts of the slip ring and brush tend to wear through repeated use, tend to fail to provide good electrical contact, and hence are unable to operate stably for a long period of time. A plurality of such slip ring mechanisms would be required to protect against malfunctioning of the air bag system. The known mechanism is also disadvantageous in that abrasive contact between the brush and the slip ring causes wearing thereof into metal powder which is liable to cause short-circuiting, the brush and slip ring generates noise signals which adversely affect a supplied pulse signal and hence invite malfunctioning of the air bag system, and there is a tendency to produce sparks between the brush and the slip ring. The connector device suffering from these difficulties is not considered optimum for use with the air bag system which is a most important safety device that is required to be absolutely reliable and stable in operation.
The present applicant has proposed an electrical connector device designed to eliminate the difficulties experienced with the slip ring connector mechanism, and comprising upper and lower casings and an electrical conductor in the form of a cord loosely spirally coiled between the upper and lower casings. One of the casings is coupled to a rotatable member such as a steering wheel and the other casing is coupled to a fixed member such as a steering column. When the rotatable member rotates, the electrical conductor is moved in the winding or unwinding direction while maintaining electrical connection between the rotatable and fixed members. Winding or unwinding movement of the coiled conductor, however, imposes a certain limitation on the extent of rotation of the steering wheel. The electrical conductor is limited in length due to a space available between the casings and a space surrounding the latter. In addition, the conductor should be assembled in position so that it is coiled in a neutral position, that is, it is not displaced in either the winding or unwinding direction when the steering wheel is not rotated. If the conductor were not coiled in its neutral position or pre-biased as assembled, it would cause the steering wheel to become sluggish when the latter is turned clockwise or counterclockwise, tensioning the conductor excessively. Assembling operation of such connector device is tedious and complex because the conductor needs to be checked for being coiled in the neutral position as assembled. There is always a tendency for the conductor to be assembled or coiled improperly since it is difficult to completely eliminate assembling errors.
The present invention effectively overcomes the foregoing problems of the prior connector devices.